This invention relates to certain Group 3, 4 or Lanthanide metal complexes possessing two metal centers in which both metal centers are activated so as to possess at least partial ligand separation or ion formation. The invention further relates to polymerization catalysts comprising the foregoing metal complexes possessing two metal centers, use thereof in addition polymerizations to prepare olefin polymers, and the resulting olefin polymers, particularly polymers having improved physical properties.
Biscyclopentadienyl Group 4 transition metal complexes in which the metal is in the +4, +3 or +2 formal oxidation state, and olefin polymerization catalysts formed from such by combination with an activating agent, for example, alumoxane or ammonium borate, are well known in the art. Thus, U.S. Pat. No. 3,242,099 describes the formation of olefin polymerization catalysts by the combination of biscyclopentadienyl metal dihalides with alumoxane. U.S. Pat. No. 5,198,401 discloses tetravalent biscyclopentadienyl Group 4 transition metal complexes and olefin polymerization catalysts obtained by converting such complexes into cationic forms in combination with a non-coordinating anion. Particularly preferred catalysts are obtained by the combination of ammonium borate salts with the biscyclopentadienyl titanium, zirconium or hafnium complexes. Among the many suitable complexes disclosed are bis(cyclopentadienyl)zirconium complexes containing a diene ligand attached to the transition metal through .sigma.-bonds where the transition metal is in its highest formal oxidation state. R. Mulhaupt, et al., J. Organomet. Chem., 460, 191 (1993), reported on the use of certain binuclear zirconocene derivatives of dicyclopentadienyl-1,4-benzene as catalysts for propylene polymerization.
Constrained geometry metal complexes, including titanium complexes, and methods for their preparation are disclosed in U.S. application Ser. No. 545,403, filed Jul. 3, 1990 (EP-A-416,815); U.S. Pat. No. 5,064,802, U.S. Pat. No. 5,374,696, U.S. Pat. No. 5,055,438, U.S. Pat. No. 5,057,475, U.S. Pat. No. 5,096,867, and U.S. Pat. No. 5,470,993.
Metal complexes of the constrained geometry type containing two metal centers joined by means of a dianionic ligand separate from and unconnected to the ligand groups in such complexes that contain delocalized 7-electrons, are previously taught, but not exemplified, in U.S. Pat. No. 5,055,438.